The invention relates to a packaged microcircuit, more particularly, to a packaged thin film microcircuit, and a method for assembling a thin film microcircuit in such a package.
There are now available high precision thin film resistor microcircuits and thin film hybrid microcircuits of resistors with bonding pads for attachment to capacitors and integrated circuits. A microcircuit chip is formed by depositing a film from two hundred to three hundred Angstroms in thickness on a substrate a few hundredths of an inch in thickness. Thin film resistive microcircuits have been designed to meet extremely low tolerances. While these circuits perform to specification in the laboratory, proper packaging is necessary for these microcircuits to perform satisfactorily in operating environments.
Besides temperature, humidity, vibration and fatigue, these microcircuits must be protected from stress and strain, if they are to perform within specification limits. In electrical devices such as disclosed in Beckman et al, U.S. Pat. No. 3,873,890, a relatively thick substrate is employed which resists deflection or deformation resulting from stress applied to the leads. In typical thin film microcircuits stress applied to the leads can deflect or deform the relatively thin substrate a slight amount if the leads are soldered or otherwise connected in a conventional manner to terminals on the microcircuit chip. This deformation, in turn, is transferred to the elements of the microcircuit itself, causing a variance in resistance due to the change of shape of the resistive film. Even the seemingly slight mechanical stress and strain applied to the leads during insertion into a circuit board can cause unacceptable changes in resistance unless measures are taken in the packaging of the microcircuit chip to insulate it from stress and strain.
In the prior art a technique called "wire bonding" is well known. In wire bonding a relatively smaller microcircuit is disposed on a relatively larger substrate and fine metallic wires, usually made of gold or aluminum, are formed on the substrate to connect the microcircuit to a set of terminals disposed along an edge of the substrate. In packaging the microcircuit and substrate, leads are soldered to the terminals. In this arrangement stress applied to the leads may be applied to the substrate, but the deformation or deflection of the substrate occurs near its edges, rather than in the center of the substrate where the circuit is disposed.
Another prior art technique for protecting the microcircuit and substrate from stress applied to the leads is described in Glickman, U.S. Pat. No. 3,320,351, where a plurality of metallic leads are rigidly connected to a metal housing by a fused glass seal.
The described prior art techniques protect the microcircuit from external stress to some extent; however, a need remains for a simple, inexpensively packaged microcircuit having a housing of insulating material in which the microcircuit substrate and connections thereto are protected from stress applied to the leads and other adverse conditions.